Embodiments of the present invention relate to removing silicon oxycarbide from substrates, particularly in the reclaiming of test substrates.
In fabricating electronic devices, various materials may be deposited onto a substrate, such as a semiconductor wafer or display, or subsequently etched from the substrate to form features such as vias, dopant regions, and interconnect lines. These materials may include metal-containing materials such as for example, aluminum, copper, tantalum, tungsten, as well as their compounds. Other materials deposited onto substrates include dielectrics such as silicon oxide or silicon nitride, and low-k (low dielectric constant) materials to separate layers of wiring and patterning from each other. These various materials may be deposited using a variety of techniques including sputtering (also referred to as physical vapor deposition or PVD), chemical vapor deposition (CVD) and thermal growth. In addition to depositing materials, other fabrication processes may be performed including doping semiconductor layers with impurities, diffusion, ion implantation, etching, chemical and mechanical polishing (CMP), cleaning, and heat treatments.
In these fabrication processes, test substrates comprising silicon wafers are often used to ensure that the processes are operating within the appropriate specifications. Rather than discard the used test substrates after they have been used to test a particular process, the used test substrates can be reclaimed. The reclamation process typically includes removing a deposited layer or material, and optionally, even removing some of the underlying silicon material so that the remaining silicon material of the test substrate is clean and substantially free of added materials or other contaminants. As a consequence, the reclamation process is intended to restore the test substrate to the same specifications as a new test substrate.
Conventional methods for reclaiming a test substrate include techniques such as, for example, chemical etching, grinding, or polishing. Wet chemical etching generally involves dipping the substrate into acidic or basic baths to remove the unwanted material from a substrate. Dry chemical etching, also known as plasma etching, involves the removal of unwanted material from a substrate through exposure to plasma gases in a vacuum chamber. Grinding and polishing involve the removal of layers of deposited material using grinding media and polishing slurries to flatten and thin out the substrate.
In the reclaiming of test substrates, it is particularly difficult to remove deposited silicon oxycarbide because it has both inorganic and carbon components, comprising, for example, amorphous silicon oxide with high carbon content, and which may comprise other materials, such as nitrogen and hydrogen. Silicon oxycarbide can be used as a low dielectric constant material (silicon oxycarbide) when it has a composition that provides a low dielectric constant (k) of less than about 3.5. Low-k dielectrics reduce the RC delay time in integrated circuits allowing corresponding increases in metal interconnect density, and thus, ever smaller circuitry. Accordingly, the deposition of low-k dielectrics such as silicon oxycarbide is important for the fabrication of ever smaller and finer circuits having feature sizes of less than 90 nm. In these deposition processes, test substrates are used to ensure the deposition of silicon oxycarbide having specified low-k properties on the substrate.
It is desirable to reclaim and reuse the test substrates that are used in testing silicon oxycarbide processes. However, conventional silicon oxycarbide removal processes often fail to suitably remove the material from the test substrates. For instance, silicon oxycarbide materials are often difficult to remove chemically, as the combination of organic and inorganic elements renders the material less reactive to chemical compositions, and such compositions can leave a gummy residue on the substrate. Also, conventional means such as grinding and polishing can cause the substrate to warp from the uneven pressures applied to the substrate. Polishing can also cause excessive scratches on the substrate surface or subsurface lattice damage. Such surface damage undesirably affects subsequent deposition process characteristics of the substrate surface, thereby altering deposition process results. As such, conventionally reclaimed substrates are often only suitable as mechanical-grade testing wafers, for example, for robot testing to evaluate accurate wafer positioning, but may not be suitable as test-grade substrates for evaluating deposition or etching processes. Conventional removal methods can also erode away an excessive amount of the substrate surface, limiting the number of times a test substrate can be reclaimed and re-used, before the substrate has to be disposed. Accordingly, conventional silicon oxycarbide removal techniques often do not provide satisfactory removal of these materials to allow re-use of the test substrates.
It is therefore desirable to remove silicon oxycarbide from a substrate with a process that can remove both the inorganic and carbon components of the silicon oxycarbide material. It is also desirable to have a removable method which does not cause warpage, surface scratches, or sub-surface damage of the substrate. It is further desirable to be able to cost effectively remove the silicon-oxycarbide in a production worthy process.